What people call a delegate in C# is what C++ people call a Functor. Obviously we will use functors, then. Note that for people actually reading all those links: in C# the Action<T> and Func<T,G> are basically also C# delegates (or, functors, if you fancy C++’s names for this more).

Okay, so how do we use this? First we make a ViewModel. Because in this case we will define the command in C++. That probably means you want a ViewModel.

I added a CompositeCommand in the mix. For a Q_PROPERTY isn’t a CommandProxy really needed, as ownership stays in C++ (when for example you pass this as parent). For a Q_INVOKABLE you would need it to wrap the QSharedPointer<AbstractCommand>.

Note. I already hear you think: wait a minute, you are not passing this to the QObject’s constructor, it’s not a QScopedPointer and you have a new but no delete. That’s because CommandProxy converts the ownership rules to QQmlEngine::setObjectOwnership (this, QQmlEngine::JavaScriptOwnership) for itself. I don’t necessarily recommend its usage here (for it’s not immediately clear), but at the same time this is just a demo. You can try printing a warning in the destructor and you’ll see that the QML garbage collector takes care of it.

The ICommand defines two things: a canExecute property and an execute() method. The CompositeCommand allows you to combine multiple commands together, the DelegateCommand makes it possible to pass two delegates (functors or lambda’s); one for the canExecute evaluation and one for the execute() method.

The idea here is that you want to make it possible to put said commands in a ViewModel and then data bind them to your View (so in QML that’s with Q_INVOKABLE and Q_PROPERTY). Meaning that the action of the component in the view results in execute() being called, and the component in the view being enabled or not is bound to the canExecute bool property.

In QML that of course corresponds to a ViewModel.cpp for a View.qml. Meanwhile you also want to make it possible to in a declarative way use certain commands in the View.qml without involving the ViewModel.cpp.

So I tried making exactly that. I’ve placed it on github in a project I plan to use more often to collect MVVM techniques I come up with. And in this article I’ll explain how and what. I’ll stick to the header files and the QML file.

Let’s make a QUndoCommand that uses a timer to simulate asynchronous behavior. We could also use QtConcurrent’s run function to use a QThreadPool and QRunnable instances that also implement QFutureInterface, of course. Seasoned Qt developers know what I mean. For the sake of example, I wanted to illustrate that QFuture can also be used for asynchronous things that aren’t threads. We’ll use the lambda because QUndoCommand isn’t a QObject, so no easy slots. That’s the only reason (asyncexample1command.h).

Wim made a stir in the land of the web. Good for Wim that he rid himself of the shackles of social media.

But how will we bring a generation of people, who are now more or less addicted to social media, to a new platform? And what should that platform look like?

I’m not a anthropologist, but I believe human nature of organizing around new concepts and techniques is that we, humans, start central and monolithic. Then we fine-tune it. We figure out that the central organization and monolithic implementation of it becomes a limiting factor. Then we decentralize it.

The next step for all those existing and potential so-called ‘online services’ is to become fully decentralized.

Every family or home should have its own IMAP and SMTP server. Should that be JMAP instead? Probably. But that ain’t the point. The fact that every family or home will have its own, is. For chat, XMPP’s s2s is like SMTP. Postfix is an implementation of SMTP like ejabberd is for XMPP’s s2s. We have Cyrus, Dovecot and others for IMAP, which is the c2s of course. And soon we’ll probably have JMAP, too. Addressability? IPv6.

Why not something like this for social media? For the next online appliance, too? Augmented reality worlds can be negotiated in a distributed fashion. Why must Second Life necessarily be centralized? Surely we can run Linden Lab’s server software, locally.

Simple, because money is not interested in anything non-centralized. Not yet.

In the other news, the Internet stopped working truly well ever since money became its driving factor.

ps. The surest way to corrupt a youth is to instruct him to hold in higher esteem those who think alike than those who think different. Quote by Friedrich Nietzsche.

Combining QFuture with QUndoCommand made a lot of sense for us. The undo and the redo methods of the QUndoCommand can also be asynchronous, of course. We wanted to use QFuture without involving threads, because our asynchronosity is done through a process and IPC, and not a thread. It’s the design mistake of QtConcurrent‘s run method, in my opinion. That meant using QFutureInterface instead (which is undocumented, but luckily public – so it’ll remain with us until at least Qt’s 6.y.z releases).

So how do we make a QUndoCommand that has a undo, and that has a redo method that returns a asynchronous QFuture<ResultType>?

We just did that, today. I’m very satisfied with the resulting API and design. It might have helped if QUndoStack would be a QUndoStack<T> and QUndoCommand would have been a QUndoCommand<T> with undo and redo’s return type being T. Just an idea for the Qt 6.y.z developers.

We are making an editor for industrial uses at Heidenhain. This is to make big Klartext programs, editable. I’m sure other industries could also use that.

Nowadays these programs often come out of a conversion from a CAD-CAM format. Before you can mill and turn your pesky military secrets on one of the machines controlled by a Heidenhain set, you’ll have to tweak the program that you converted from your CAD-CAM product. We are making the editor for that.

We’re also making the overlaying (the changes made by the user) undoable. The APIs for that kinda look like this. All examples on my blog are amateur extracts of the real thing, of course.

I feel like it’s actually going to work out. Architecturally and organizationally the other developers in our team are getting at the right level of expertise and sense of wanting this.

That is most important for anything to make it happen.

It feels a bit like how Nokia was: I’m learning a lot about myself from techleading: how to propose a design, concept or idea; how to convince deeply technical people; how to push others to go further than what they can already do. How to make a team quit competing and start sharing a common goal. The infrastructure for that was provided to me by Nokia. At Heidenhain, I feel like having played a small role in it.

Among the problems we’ll face is that we want asynchronous APIs that are undoable and that we want to switch to read only, undoable editing, non-undoable editing and that QML doesn’t really work well with QFuture. At least not yet. We want an interface that is easy to talk with from QML. Yet we want to switch between complicated behaviors.

We will also want synchronous mode and asynchronous mode. Because I just invented that requirement out of thin air.

Ok, first the “design”. We see a lot of behaviors, for something that can do something. The behaviors will perform for that something, the actions it can do. That is the strategy design pattern, then. It’s the one about ducks and wing fly behavior and rocket propelled fly behavior and the ostrich that has a can’t fly behavior. For undo and redo, we have the command pattern. We have this neat thing in Qt for that. We’ll use it. We don’t reinvent the wheel. Reinventing the wheel is stupid.

Let’s create the duck. I mean, the thing-editor as I will use “Thing” for the thing that is being edited. We want copy (sync is sufficient), paste (must be aysnc), and edit (must be async). We could also have insert and delete, but those APIs would be just like edit. Paste is usually similar to insert, of course. Except that it can be a combined delete and insert when overwriting content. The command pattern allows you to make such combinations. Not the purpose of this example, though.

Enough explanation. Let’s start! The ThingEditor, is like the flying Duck in strategy. This is going to be more or less the API that we will present to the QML world. It could be your ViewModel, for example (ie. you could let your ThingViewModel subclass ThingEditor).

For the implementation of this class, I’ll only provide the non-obvious pieces. I’m sure you can do that setThing, setEditingBehavior and the constructor yourself. I’m also providing it only once, and also only for the EditCurrentCommand. The one about paste is going to be exactly the same.

For QUndo we’ll need a QUndoCommand. For each undoable action we indeed need to make such a command. You could add more state and pass it to the constructor. It’s common, for example, to pass Thing, or the ThingEditor or the behavior (this is why I used QSharedPointer for those: as long as your command lives in the stack, you’ll need it to hold a reference to that state).

You can (and probably should) also make this one abstract (and/or a so called pure interface), as you’ll usually want many implementations of this one (one for every kind of editing behavior). Note that it leaks the QUndoCommand instances unless you handle them (ie. storing them in a QUndoStack). That in itself is a good reason to keep it abstract.

And now we can make the whole thing undoable by making a undoable editing behavior. I’ll leave a non-undoable editing behavior as an exercise to the reader (ie. just perform redo() on the QUndoCommand, don’t store it in the QUndoStack and immediately delete or cmd->deleteLater() the instance).

Note that if m_synchronous is false, that (all access to) m_undoStack, and the undo and redo methods of your QUndoCommands, must be (made) thread-safe. The thread-safety is not the purpose of this example, though.

Funny how even the software developers at the CIA have problems with idiots who want to put binaries in git. They also know about Git-Flow, my preferred git branching workflow. I kind of wonder how come, if they know about Git-Flow, we see so few leaked NSA and CIA tools with correct semver versioning. Sometimes it’s somewhat okayish, like you can see here. But v1.0-RC3 is not really semver if you see how they got there here. To start with, your alpha versions start with 0.0.x. So where are all those versions under 0.0.x that happened before release candidate 3? 1.0, 1.1-beta, 1.0-phase2, 1.0-beta1-, 1.0-beta-7. WTF guys. That’s not a good versioning scheme. Just call it 0.0.1, 0.0.2, 0.1.0, 0.1.1, 0.1.2 for the betas. And when the thing sees first usage, start calling it 1.0.0, 1.0.1, 1.0.2, 1.1.0, 1.1.1, 1.2.0 etc. What’s wrong with that? And how are all these words like alha-1, beta-2, phase2, etc any better? Maybe just fire your release maintainer! Admittedly for that 2.0.x series they at least tried to get it right.

The point is that packaging tools can be configured to let other packages depend on these version numbers. In x.y.z the x number has implications on API incompatibility whereas the y number can be used for compatible feature additions.

I can imagine that different malwares, exploits, rootkits, intrusion tools they develop would pose incompatibilities with each other, and that for example the NSA and CIA want to share libraries and link without having to recompile or repackage. So versioning to indicate ABI and API compatibility wouldn’t be a bad idea. Let’s hope in the next round of massive leaks we see them having learned good software development processes and practices.

As a freelancer I saw many companies, many situations and worked with many Project Managers, Product Owners, Scrum Masters and god knows what names the HR department came up with.

What is most important, in my experience, is that the people leading the team try to focus the people in the group on as few common goals as possible during one sprint. The more stories or goals the team has to finish, the more individualism and the fewer things will get done (with done being defined by your definition of done).

Differently put you should try to make your team work like how a soccer team plays. You try to make three, four or five goals per sprint. But you do this as a team.

Example: When a story isn’t finished at the end of the sprint; it’s the team’s fault. Not the fault of the one guy that worked on it. The team has to find a solution. If it’s always the same guy being lazy, that’s not the project’s or the team’s results. You or HR deals with that guy later. Doing so is outside of Scrum’s scope. It’s not for your retrospective discussion. But do sanction the team for not delivering.

Another example is not to put too much stories on the task board and yet to keep stories as small and/or well defined as possible. Too much stories or too large stories will result in every individual picking a different story (or subtask of the larger story) to be responsible for. At the end of the sprint none of these will be really finished. And the developers in the team won’t care about the other features being developed during the sprint. So they will dislike having to review other people’s features. They’ll have difficulty finding a reviewer. They won’t communicate with each other. They’ll become careless and dispassionate.

Your planning caused that. That makes you a bad team player. The coach is part of the team.

Like I mentioned a few months ago, here we are again. More things equals more crap on the Internet. Not more utility. No. More crap. It’s only crap. With lower case ‘c’. The crap of the crap programmers of the crap is not worth wasting an expensive capital letter on.